Summary of work in progress includes the following. 1) Further define the x-ray induced G block in terms of biochemical markers and ultrastructural changes. 2) Study the x-ray sensitivity during the cycle for induction of mutations with emphasis on studying the different spectra of mutants during the cycle. 3) Study the effects of ionizing radiation on the attachment of DNA to the nuclear membrane. 4) Study the effects of different times and temperature variations on hyperthermic radiosensitization during different phases of the cell cycle.